Study of Impulse Forcing on a Simply Supported Blade

Abstract

Results from a series of low-speed wind-tunnel experiments are presented showing the influence of aperiodic forcing on the vibratory and strain response of a simply supported blade. Blade forcing was accomplished via both mechanical and aerodynamic means. Variable amplitude/frequency mechanical forcing was achieved through an electromagnetic shaker, while aerodynamic forcing corresponded to wake shedding from an upstream cylinder. Measured blade-strain probability distributions are presented illustrating the parametric dependencies of blade-strain on freestream velocity, forcing frequency, and forcing amplitude whether the forcing is mechanical, aerodynamic, a combination. These distributions suggest impulse forcing broadens blade-strain probability distributions, producing higher strain values. Impulse forcing frequency significantly impacted blade-strain distribution, while impulse amplitude and coherence were not nearly as influential. Aerodynamic forcing dominated the effects of the examined mechanical forcing, promoting a randomly distributed blade strain about its mean, approximately equal to a bell shaped strain response.